Gelatin is a partially hydrolyzed derivative of collagen protein (pretreat and boil animal by-products and you get gelatin). Powdered gelatin is simply gelatin grinded into a fine powder. Most widely recognized as the compound that makes jello gel, and as the base of naturally nutrient dense bone broth.
Gelatin powder poured into hot water will dissolve as its hydrogen bonds that maintained the compounds triple helix structure are broken by rapidly moving water molecules. The polypeptide chains no longer connected to each other are then free to spread out in the liquid. Then, when you allow the water to cool the polypeptide chains of the gelatin will begin re-attaching themselves in a disorderly mesh trapping water molecules and forming the well known semi-solid gel. Gelatin based gel is semi-solid at room temperature, will freeze at or below 32 degrees Fahrenheit, and will melt at or above 95 degrees Fahrenheit.